Apparatus for testing and calibrating watt-hour meters



May 23, 1950 R. T. FENN 2,508,505

APPARATUS FOR TESTING AND CALIBRATING WATT-HOUR METERS Filed Oct. 19,1945 INVENTOR Raymond T Penn y @M I ATTORNE Patented May 23, 1950APPARATUS FOR TESTING AND CALIBRAT- ING WATT-HOUR METERS Raymond T.Fenn, Springfield, Vt.

Application October 19, 1945, Serial No. 623,355

1 Claim.

The present invention relates to an improved method of and apparatus fortesting and calibrating watthour meters of the type commonly employed bycommercial distributors of electrical power for measuring the amount ofelectrical energy consumed by customers. The object of the invention isto provide an arrangement for conveniently testing and calibrating awatthour meter at the place where it is installed on the premises of acustomer, thereby eliminating the usual practice of periodicallyremoving such meters from customers premises to a central location wheretesting equipment is maintained by the power distributing company.

According to the present invention, a standard watthour meter can betested at the place where it is installed and its actual operation underload visually checked with the operation of a master meter, by providingthe meter under test with a simple attachment in the form of a lightreflecting device, the functioning of which can be readily compared withthe functioning of a similar device on the master meter. By reason ofthe simplicity and portability of my improved testing equipment, it ispossible to quickly test and adjust a consumers watthour meter at theplace where it is installed, so that the meter will thereafter operatewith a high degree of accuracy in the measurement of consumers current.

The above and other advantageous features of the invention willhereinafter more fully appear from the following description, consideredin connection with the accompanying drawings, in which:

Fig. 1 illustrates the external appearance of a conventional customerswatthour meter, in association with the portable testing apparatus and amaster meter.

Fig. 2 is a diagrammatic view illustrating the performance of a test inaccordance with the practice of the invention.

Fig. 3 is a diagrammatic view showing a modification of the arrangementof Fig. 2.

Referring to the drawing, Fig. 1 illustrates the appearance of aconventional watthour meter M, as installed in a customers premises oradjacent thereto, with the meter M providing the usual integratingmechanism and recording dials l for indicating the amount of powerconsumed. The meter M provides the usual shaft 2 carrying a disk 3 whichrotates at a speed determined by the amount of current consumed to drivethe integrating mechanism. In order that the dials of the meter M may beconveniently read from time to time, the mechanism of the meter isenclosed in a glass casing l, so that the rotor disk 3 is also visibleat all times, with the disk 3, theoretically at least, being at restwhen no power is being consumed. v

The test arrangement of the present invention makes use of the fact thatthe meter cover 4 is readily removable in any location where the meter Mmay be installed, and where adjustments to the meter may be made. Forthe purpose of test-- ing, the shaft 2 of the meter M is provided with areflector 5 presenting a series of plane reflecting surfaces 6 arrangedabout the axis of the shaft. Consequently, these reflecting surfaces 6will successively come into view from a point adjacent the meter,whenever the meter shaft 2 rotates by reason of passage of currentthrough the meter M.

Referring now to Fig. 2, the arrangement of the present invention alsocontemplates the employment of a portable testing assembly or panel P inassociation with the meter M to be tested,

the panel P being indicated diagrammatically by dot and dash lines. Thepanel may be conveniently attached to meter M by the cover attachingdevices and provides means for utilizing the reflector 5 on the metershaft for testing and calibrating the meter M Where it is installed. Forthis purpose, the panel P provides a light source I in the form of alamp of known wattage, which light source is adapted to transmit lightrays through a lens 8 mounted on the panel P so as to strike thereflecting surfaces 6 of the reflector 5 whenever the shaft 12 rotates.Reflected light rays from the meter M undertest are adapted to impingeupon a photoelectric cell 9, also mounted on the panel P, and electricalimpulses from the cell 9 are adapted to be carried by conductors IE! toa suitable electronic amplifier II, which forms part of testingequipment mounted on a panel P that is associated with a master meter M.

This master meter M has been carefully checked with known standards asto the accuracy of its readings, so that its operation may be used tocheck the accuracy of any installed meter, such as the meter M. Themaster meter M may be of any suitable type and, for purposes ofillustration, it is shown with its rotor shaft 2' provided with areflector 5' similar to the reflector 5, in that it presents a series ofplane reflecting surfaces 6' arranged about the axis of the rotor shaft2. The testing panel P further provides a light source 1' and a lens 8'is adapted to project light rays from the source 1' so as to strike thesurfaces 6' of thereflector as the rotor shaft 2' rotates. For purposesof illustration, the number of surfaces 6 and 6' on the reflectors 5 and5' is shown as being the same, although this is not essential, asexplained hereafter.

.The panel P also carries a translucent screen l2 mounted where it maybe readil observed, and arprojected light ray from the source l" will bereflected so asto appear as a light spot S substantially centered on thescreen l2, as indicated. With the arrangement described thus far inconnection with the master meter M, rotation of the master meter shaft2' will. cause the lightspot S to be intermittently flashed on thescreen 12 as the projected light ray from the source I successivelyimpinges upon the revolving surfaces 6' of the reflector 5. Obviously,this. intermittent appearance of the light spot S on the screen l2 willcontinue at a rate dependent upon the speed of the master meter shaft 2,as long as the shaft rotates, and in theabsence of any factorsafiectin'g the continuous transmission of light 7 rays from the sourcel-"I to the reflector 5'.

As previously pointed out, electrical impulses from the photoelectriccell 9 are adapted to be stepped up by the amplifier I I mounted on thepanel P. The output of the amplifier H is adapted to energize a solenoidl3, and with the arrangement previously described with reference to thepanel P, the solenoid It will be energized each time a light ray istransmitted to the cell 9 from the source I, as a result of revolutionof the reflecting surfaces 6 with the shaft 2 of the meter M that is tobe'tested.

The magnetic armature or plunger It of the solenoid operates a slidablymounted shutter or light gate [-5 having an opening H5 through which alight ray from the source I may pass to the reflector 5' when thesolenoid I3 is energized. However, should the solenoid be deenergized,the light gate i5 will block the light ray and it is obvious that theparticular moment at which the opening it permits: the passage of thislight ray will determine the angle of incidence of the ray with areflectorsurf'ace 6-.

As shown in Fig. 2, the light gate 5 is open at the same moment the rayfrom the light source I is striking a reflector surface 8', so that therefl'ectedlight spot S is centeredon the screen l2. However, should thelight gate it be opened either in advance of or after the reflector 5 onthe master meter M reaches thev position of Fig. 2, the light spot Swill appear to one side or the other of the center of the screen i2.

When it is desired to check and calibrate an installed meter M which haspreviously been provided with a reflector 5, the arrangement is set 1are not illuminated, by reason of the fact that the control switch I!for the test panels is then open. However, when the switch I! is closedto connect the panels to a commercial power source as indicated, bothmeters M and M'- are subjected to the same electricalload, and bothlight sources T and 1' are illuminated.

' Therefore, when the reflector 5' of the master meter M" starts torotate, the light gate hasv already been opened by the initiallyreflected ray of light from thesource l to the cell 9. Assuming thenthat the meter M under test is accurate,

At this time both reflectors 5 and 5' will turn at exactly the samerate, and the gate opening I6 will permit passage of the ray from thesource 1 at such an angle with respect to th reflecting surfaces 6' asto cause the light spot S to appear intermittently in the center of thescreen I2. The light spot S will appear on the screen with a frequencydependent upon the rate of movement of the reheater 5', which isdirectly'relatecl to the speed of the master'meter M, and if the meter Munder test is rotating in exact synchronism with the master meter, itfollows that the light spot S will appear successively in the same placeon the screen l2. However, should the meter M under test be running theleast bit fast or slow, as compared to the master meter M, successiveenergizations of the solenoid I3 by the photoelectric cell 9 will be outof step with the movement of the reflector 5 on the master meter.

The net result will be to shift the light spot S tothe right'or to theleft of the center of the screen l2, due to the amount that the lightgate operation is out of phase'with the successive arrivals of thereflector surfaces 6 in line with the axis of the projecting lens 8.Therefore, when the meter M under test is not in synchronism, successiveappearances of the lightspot S will trace a path across the screen l2,with the direction of this: apparent travel of the spot to one side orthe other of the screen center indicatin whether the meter under test isrunning faster or slower than the master meter.

Assuming that a test of an installed meter has been carried on asdescribed above, the person making the test will obtain a graphicvisual'indication on the screen 12 as to the degree to which the meterunder test may be running fast or slow. Obviously, the meter tester canmake slight adjustments to the meter undertest in order to correct-' anyfast or slow tendency and, by continuing the tests, quickly determinewhether or not the adjustments have been properly made. All theseoperations may be per formed without removing the meter under test fromits place of installation. Or, if a meter under test appears to be sobadly out of adjustment as to necessitateits' removal, obviousl areplacement meter canrbe installed and quickly checked as to itsaccuracy by performing the same steps outlined above and observing theposition of the light spot 8- on the screen I 2.

While the equipment on'the panels P and P" is shown and described asbeing associated with the meters M and M, respectively, obviously theapparatus for carrying out the invention is susceptible of beingarranged ina difierent manner to obtain substantially the same results.For example, there is shown in- Fig. 3 a modified arrangement, whereinthe panel P with the amplifier H, observing screen l2 and light gate I5is installed in association. with the meter M to be tested. Similarly,the panel P with the light source 'I and photoelectric cell 9 isassociated with the master meter M. This modified arrangement possessescertainadvantages over the arrangement of. Fig. 2, in that the personmaking the test can observe-the screen is while making any necessaryadjustments required for the meter under test, without having hisattention distracted by referring to the master meter. In other words,

the modified arrangement of Fig. 3' makes it readily possible to test ameter installed in a place where it'might be difficult to mount themaster meter, withthe length of the conductors I 0 between thephotoelectric: cell 9 and the amplifler I l making possible any desiredspacing between the panels P and P to meet conditions of the test.

As previously pointed out, while the number of reflecting surfaces 8 andB on the reflectors 5 and 5 is shown as being the same for purposes ofillustration, this is not essential and will depend upon the meterconstants. That is to say, if the meter M under test and the mastermeter M make the same number of revolutions per watthour, the number ofreflecting surfaces 6 and 6 will be the same. If, however, the metershafts 2 and 2' run at diiferent base speeds, the number of surfaces 6and 6 on the reflectors will be determined from the least commondenominator of these speeds. With any relation, the mode of testing andcalibrating the customers meter remains the same.

From a consideration of the foregoing, it is apparent that the practiceof the present invention permits a customer's watthour meter to betested and calibrated where it is installed, so that the complaint ofany customer can be quickly checked and remedied in the presence of thecustomer, if desired. Thus in cases where the customer complains ofbeing overcharged for electrical energy, and the meter indicates moreenergy than actually passes through it, it is desirable to determine theactual percentage of error at the time of test. In this case, a variableratio transmission can be provided between the shaft 2 of the mastermeter M and its reflector 5, and the ratio would be adjusted until themeters appear to be indicating exactly the same. The amount ofadjustment to obtain this result would then indicate the percentageerror of the customers meter M, and such an adjustment can 6 .be readilymade with the meter cover removed and while the test panel P is attachedto the meter as previously described.

I claim:

In combination, first and second rotatable ele ments each having aplurality of substantially flat light-reflecting areas circumferentiallyspaced about the periphery thereof, first and second light sources eachdirecting its rays toward a respective one of said rotatable elements, ascreen positioned to receive light rays reflected from said firstrotatable element, a stationary light-sensitive cell positioned forreceiving intermittent flashes of reflected light rays from said secondrotatable element, a vibratory light gate interposed between said firstlight source and said first rotatable element, and means controlled bysaid light-sensitive cell for actuating said gate back and forth intimed relation with the intermittent flashes received by said cell fromsaid second rotatable element thereby to project intermittent flashes oflight from said first light source upon said first rotatable element.

RAYMOND T. FENN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,819,494 Aronoif Aug. 18, 19311,853,657 Bradshaw et a1 Apr. 12, 1932 1,864,677 Sparkes June 28, 19321,878,658 Aronoff Sept. 20, 1932 1,889,128 McClintock Nov. 29, 19321,949,743 Holmes Mar. 6, 1934-

